Hydrogen-storing carbonaceous material and method for producing the same, hydrogen-stored carbonaceous material and method for producing the same and battery and fuel cell using hydrogen-stored carbonaceous material

ABSTRACT

A hydrogen-storing carbonaceous material is provided. The hydrogen-storing carbonaceous material is obtained by heating a carbonaceous material in a gas atmosphere including hydrogen gas and substantially including no reactive gas as impurity gas to store hydrogen. According to the present invention, since the surface of the carbonaceous material can be cleaned and hydrogen can be stored in the carbonaceous material in the same gas atmosphere and a hydrogen-stored carbonaceous material can be produced by controlling a heating process time in the gas atmosphere including the hydrogen gas and substantially including no reactive gas as the impurity gas. This can facilitate the use of the hydrogen-stored carbonaceous material as applied to devices, systems, processes and/or the like.

RELATED APPLICATION DATA

The present application claims priority to Japanese Patent ApplicationNo. P2000-074407 filed on Mar. 16, 2000, herein incorporated byreference to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a hydrogen-storing carbonaceousmaterial and a method for producing it, a hydrogen-stored carbonaceousmaterial and a method for producing it and a battery and a fuel cellusing a hydrogen-stored carbonaceous material, and more particularly toa hydrogen-storing carbonaceous material and a method for producing it,a hydrogen-stored carbonaceous material and a method for producing itand a battery using the hydrogen-stored carbonaceous material and a fuelcell using the hydrogen-stored carbonaceous material.

Fossil fuel such as gasoline, light oil, or the like have been readilyemployed as the energy source for producing an electric power as well asthe energy source of motor vehicles or the like. The fossil fuel notonly may possibly degrade a global environment, but also is exhaustibleand dubious whether or not the fossil fuel can be stably supplied.

Hydrogen has been paid attention to in place of the fossil fuel havingthe above described problems. The hydrogen is contained in water,inexhaustibly exists on the earth and includes a large quantity ofchemical energy per amount of material. Further, the hydrogen hasadvantages as a clean and inexhaustible energy source by which thefossil fuel is replaced, because the hydrogen does not discharge harmfulsubstances or global greenhouse gas or the like when it is used as theenergy source.

Especially recently, the fuel cell that an electric energy can begenerated from the hydrogen energy has been eagerly studied anddeveloped and it has been expected that the fuel cell is applied to alarge-scale power generation, an onsite private power generation, andfurther, to a power supply for a motor vehicle.

On the other hand, since the hydrogen is gaseous under ambienttemperature and ambient pressure, it is treated with more difficultythan liquid or solid. Since the density of the gas is extremely small ascompared with that of liquid or solid, the chemical energy of the gas issmall per volume. Further, it is inconveniently difficult to store ortransport the gas. Still further, since the hydrogen is gas, it isliable to leak. When the hydrogen leaks, the danger of explosion isundesirably generated, which results in a great trouble in utilizationof the hydrogen energy.

Thus, in order to put an energy system using the hydrogen energy topractical use, the development of a technique that the gaseous hydrogenis efficiently and safely stored in a small volume has been promoted.There have been proposed a method for hydrogen storage as high pressuregas, a method for hydrogen storage as liquefied hydrogen and a methodfor using a hydrogen-storing material, or the like.

In the method for hydrogen storage as the high pressure gas, since avery strong metallic pressure proof vessel such as a cylinder needs tobe used as a storage vessel, the vessel itself becomes extremely heavyand the density of the high pressure gas is ordinarily about 12 mg/cc.Accordingly, not only the storage density of the hydrogen isdisadvantageously very small and a storage efficiency is low, but alsothere has a problem in view of safety because of high pressure.

On the contrary, in the method for hydrogen storage as the liquefiedhydrogen, the storage density is ordinarily about 70 mg/cc. Although thestorage density is considerably high, it is necessary to cool hydrogendown to lower than −250° C. in order to liquefy, so that an additionaldevice such as a cooling device is required. Therefore, not only asystem has been undesirably complicated, but also energy for cooling hasbeen needed.

Further, hydrogen-stored alloys are most effective materials among thehydrogen-stored materials. For instance, there have been knownlanthanum-nickel, vanadium, and magnesium hydrogen-stored alloys. Thepractical hydrogen storage density of these hydrogen-stored alloys isgenerally 100 mg/cc. Although the hydrogen is stored in thesehydrogen-stored alloys, the hydrogen storage density of these alloys isnot lower than that of liquefied hydrogen. Therefore, the use of thehydrogen-storing materials is the most efficient among conventionalhydrogen storage methods. Further, when the hydrogen-storing alloy isused, the hydrogen can be stored in the hydrogen-storing alloy and thehydrogen can be discharged from the hydrogen-storing alloy at aroundroom temperature. Further, since the hydrogen storage condition iscontrolled under the balance of the partial pressure of hydrogen, thehydrogen-storing alloy is advantageously treated more easily than thehigh pressure gas or the liquefied hydrogen.

However, since the hydrogen-stored alloys consist of metallic alloys,they are heavy and the amount of stored hydrogen is limited toapproximately 20 mg/g per unit weight, which may not be said to besufficient. Further, since the structure of the hydrogen-storing alloyis gradually destroyed in accordance with the repeated the cycle ofstoring and discharging of hydrogen gas, a performance is undesirablydeteriorated. Still further, there may be possibly generated fears ofthe problems of resources and an environment depending on thecomposition of the alloy.

Thus, for overcoming the above described issues of the conventionalmethods for hydrogen storage, a carbon material is paid attention to asthe hydrogen-storing material.

For example, Japanese Patent Application Laid-Open No. hei. 5-270801proposes a method that the addition reaction of hydrogen is applied tofullerene to store hydrogen. In this method, since a chemical bond suchas a covalent bond is formed between a carbon atom and a hydrogen atom,this method is to be called an addition of hydrogen rather than ahydrogen storage. Since the upper limit of the amount of hydrogen whichcan be added by the chemical bonds is essentially restricted to thenumber of unsaturated bonds of carbon atoms, the amount of storedhydrogen is limited.

Further, Japanese Patent Application Laid-Open No. hei. 10-72201proposes a technique that fullerene is used as the hydrogen-storingmaterial and the surface of the fullerene is covered with catalyticmetal such as platinum deposited by a vacuum method or a sputteringmethod to store hydrogen. In order to employ platinum as the catalyticmetal and cover the surface of fullerene with it, much platinum needs tobe used so that not only a cost is increased, but also a problem isgenerated in view of resources.

The method for hydrogen storage known heretofore is difficult to say asa practical one when hydrogen energy is utilized. Especially, when thehydrogen energy is employed as an energy source for motor vehicles,marine vessels, general domestic power supplies, various kinds of smallelectric devices, or the like or when a large amount of hydrogen needsto be conveyed, the conventional methods for hydrogen storage is notpractical.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide ahydrogen-storing carbonaceous material and a method for producing it, ahydrogen-stored carbonaceous material and a method for producing it anda battery and a fuel cell using a hydrogen-stored carbonaceous materialwhich are light-weight, can be repeatedly used in a safe manner and haveminimal, if any, impact on resource and environmental concerns.

Applicants have found that the above described advantage could beachieved by the hydrogen-storing carbonaceous material obtained byheating the carbonaceous material under a gas atmosphere substantiallyincluding hydrogen gas and including no reactive gas as impurity gas.

In order to store a large amount of hydrogen in the carbonaceousmaterial, it is an important factor to increase an area where thesurface of the carbonaceous material comes into contact with hydrogenatoms or hydrogen molecules when a hydrogen storing mechanism is carriedout in the form of a chemisorption or when the storing is carried out inthe form of a proton storage or other like and suitable mechanism.Therefore, it is important to clean the surface of the carbonaceousmaterial and efficiently remove impurities on the surface. In that case,while it was possible to clean the surface of the carbonaceous materialand remove the impurities of the surface by using inert gas such asnitrogen gas, argon gas, or vacuum, it was found, according to the studyof the inventors of the present invention, that the carbonaceousmaterial was heated in the gas atmosphere including hydrogen gas withhigh reducing capacity and substantially including no reactive gas asimpurity gas so that the surface of the carbonaceous material wasefficiently cleaned and an area where the surface of the carbonaceousmaterial came into contact with the hydrogen atoms or the hydrogenmolecules could be greatly increased. The present invention was inventedon the basis of the above described knowledge.

Further, the present invention in an embodiment is designed to obtain ahydrogen-storing carbonaceous material by heating the carbonaceousmaterial under the gas atmosphere including hydrogen gas andsubstantially including no reactive gas as impurity gas.

Still further, the present invention in an embodiment relates to ahydrogen-storing carbonaceous material by heating the carbonaceousmaterial under the gas atmosphere including the hydrogen gas andsubstantially including no reactive gas as impurity gas to storehydrogen.

According to the present invention in an embodiment, since the surfaceof the carbonaceous material can be cleaned and hydrogen can be storedin the carbonaceous material in the same gas atmosphere, and ahydrogen-stored carbonaceous material can be produced simply bycontrolling a heating process time in the gas atmosphere including thehydrogen gas and substantially including no reactive gas as impuritygas, not only the structure of a hydrogen storage device can be compact,but also a hydrogen storage system and a hydrogen storage process can besimplified. Here, the heating process time required for producing thehydrogen-stored carbonaceous material can be experientially determined.

Further, the present invention in an embodiment relates to a manufacturefor a hydrogen-stored carbonaceous material obtained by heating thecarbonaceous material in the gas atmosphere including hydrogen gas andsubstantially including no reactive gas as impurity gas to storehydrogen.

Further, the present invention in an embodiment relates to a batteryhaving an anode, a cathode, an electrolyte interposed therebetween, andthe anode and/or the cathode includes a hydrogen-stored carbonaceousmaterial obtained by heating the carbonaceous material in a gasatmosphere including hydrogen gas and substantially including noreactive gas as impurity gas to store hydrogen.

In an alkaline storage battery according to the present invention in anembodiment in which aqueous alkaline solution such as potassiumhydroxide solution is employed for the electrolyte, a proton moves tothe anode from the cathode through the aqueous alkaline solution tostore the proton in the anode during a charging process. The proton canbe moved to the cathode side from the anode side through the aqueousalkaline solution during a discharging process. Further, in ahydrogen-air fuel cell in which perfluorosulfonic acid polymerelectrolyte film or the like is used for the electrolyte, a protonpreviously stored in a hydrogen electrode by a charging or storingprocess is supplied to an air electrode through the polymer electrolytefilm during the discharging process. Accordingly, in the hydrogen-airfuel cell, an electric power can be generated in a stable manner.

Further, the present invention in an embodiment relates to a fuel cellcomprising a laminated structure having an anode, a proton conductor anda cathode, and a hydrogen storage part including a hydrogen-storedcarbonaceous material obtained by heating the carbonaceous material inthe gas atmosphere including hydrogen gas and substantially including noreactive gas as impurity gas to store hydrogen, discharging the hydrogenand supplying it to the anode. Since the fuel cell according to thepresent invention has the laminated structure of the anode, the protonconductor and the cathode, and the hydrogen storage part including thehydrogen-stored carbonaceous material obtained by heating thecarbonaceous material under the atmosphere of gas including hydrogen gasand substantially including no reactive gas as impurity gas to storehydrogen, discharging the hydrogen and supplying it to the anode, thehydrogen discharged from the hydrogen storage part produces a proton inaccordance with a catalytic action in the anode. The produced protonmoves to the cathode together with a proton produced by the protonconductor so that the protons combine with oxygen to produce water andgenerate an electromotive force. Thus, according to the presentinvention in an embodiment, there can be provided the fuel cell in whichthe hydrogen can be more efficiently supplied than a case in which thehydrogen storage part is not provided and the conductivity of theprotons is high.

In the present invention, the hydrogen stored in the carbonaceousmaterial includes not only hydrogen molecules and hydrogen atoms, butalso a proton as the atomic nucleus of hydrogen.

Further, the gas atmosphere for heating the carbonaceous material in thepresent invention may include gas other than hydrogen gas as impuritygas. The impurity gas must be inert gas that exhibits no reactivity suchas nitrogen gas, helium gas, neon gas, argon gas, krypton gas, xenongas, radon gas, the like, or mixtures thereof.

In the present invention in an embodiment, the carbonaceous material isdesirably heated in the gas atmosphere that substantially includes nogas other than hydrogen gas.

According to the study of the inventors of the present invention, it isrecognized that when high heating temperature does not cause thestructural change of the carbonaceous material, the higher heatingtemperature will generate the higher effect. Since the decrease of themass of the carbonaceous material is recognized when the carbonaceousmaterial is held under the atmosphere of nitrogen gas after thecarbonaceous material is heated at about 50° C. in a gas atmosphereincluding hydrogen gas and substantially no reactive gas as impuritygas, the carbonaceous material is preferably heated at more than 50° C.

Further, according to the study of the inventors of the invention, it isrecognized that, when gas pressure is more increased, the surfacecleaning effect and the hydrogen storage effect of the carbonaceousmaterial by the gas including hydrogen gas and substantially includingno reactive gas as impurity gas will be the more improved. Therefore,the carbonaceous material is preferably heated under the gas pressure ofabout 1 atmospheric pressure or higher.

As the carbonaceous material employed for the present invention in anembodiment, a carbonaceous material having a large surface and astructural curvature is employed. According to the study of theinventors of the present invention, since the carbonaceous materialbelongs to a s-p non-orthogonal electron system, it is found that HOMOand LUMO are lower than those of a s-p orthogonal electron system.Therefore, the carbonaceous material with the curvature can become astrong electron acceptor and separate the hydrogen into an electron anda proton (atomic nucleus of hydrogen) to store the hydrogen with highdensity in the form of the proton having no volume.

Further, the carbonaceous material in the present invention in anembodiment is preferably composed of a carbonaceous material includingfullerene, carbon nanofiber, carbon nanotube, carbon soot, nanocapsule,bucky onion and carbon fiber the like or mixtures thereof. As thefullerene, any spheroidal carbon molecules may be used and allspheroidal carbon molecules having the number of carbons such as 36, 60,70, 72, 74, 76, 78, 80, 82, 84, the like or mixtures thereof can beutilized.

Still further, the carbonaceous material used in the present inventionin an embodiment includes on its surface fine particles made of metal ora metallic alloy having a function for separating hydrogen atoms fromhydrogen molecules, or further, separating protons and electrons fromthe hydrogen atoms. The average size of the fine particles made of themetal or the alloy is desirably about 1 micron or smaller. As the metal,there is preferably employed metal or an alloy including iron, rareearth elements, nickel, cobalt, palladium, rhodium, platinum or alloyscomposed of one or two or more of these metals.

When the carbonaceous material having the curvature of fullerene, carbonnanofiber, carbon nanotube, carbon soot, nanocapsule, bucky onion,carbon fiber, the like or mixtures thereof is produced by an arcdischarge method, the metal or the alloy thereof is preferably mixedinto a graphite rod before the arc discharge. At the time of the arcdischarge, the above described metals or the alloys thereof are allowedto exist, the yield of the carbonaceous material can be enhanced and thehydrogen-storing carbonaceous material with the curvature can resultfrom the catalytic action of these metals or the alloy thereof. It hasbeen known that these metals or the alloys thereof perform a catalyticaction when the carbonaceous material such as fullerene, carbonnanofiber, carbon nanotube and carbon fiber or the like is produced by alaser ablation method. The carbonaceous material such as fullerene,carbon nanofiber, carbon nanotube, carbon fiber, the like or mixturesthereof may be collected, added to and mixed with the hydrogen-storingcarbonaceous material so that the surface of the hydrogen-storingcarbonaceous material includes these metals or the alloys thereof.

In the present invention, in an embodiment, the carbonaceous materialincluding these metals or alloys thereof or the carbonaceous materialincluding no metal or no alloy carries at least on its surface metallicfine particles of about 10 wt % or less which have a catalyzing functionfor separating hydrogen atoms from hydrogen molecules, and further,separating protons and electrons from the hydrogen atoms. As apreferable metal having such a catalyzing function, there may beexemplified platinum or a platinum alloy, or the like. In order todeposit these metals on the surface of the carbonaceous material,typical methods such as a sputtering method, a vacuum deposition method,a chemical method, a mixture or the like may be used.

Further, when platinum fine particles or platinum alloy fine particlesare carried on the carbonaceous material, a method using solutioncontaining platinum complexes or an arc discharge method usingelectrodes including platinum may be applied thereto. In the method thatemploys the platinum complex solutions, in an embodiment, chloroplatinicacid solution is treated with sodium hydrogen sulfite or hydrogenperoxide, then, the carbonaceous material is added to the resultantsolution and the solution is agitated so that the platinum fineparticles or the platinum alloy fine particles can be deposited on thecarbonaceous materials. On the other hand, in the arc discharge method,the platinum or the platinum alloy is partly attached to the electrodepart of the arc discharge, and is subjected to the arc discharge to beevaporated so that the platinum or the platinum alloy can be adhered tothe carbonaceous material housed in a chamber.

The above described metals or the alloys thereof are formed on thecarbonaceous material, so that the hydrogen storage capacity can be moreimproved than that when the metals or the alloys thereof are not formedon the carbonaceous material. Further, it is found that fluorine ormolecule thereof serving as an electron donor or an amine molecule suchas ammonia is mixed or combined with the carbonaceous material toefficiently generate a charge separation.

As described above, hydrogen composed of protons and electrons issupplied to the hydrogen-storing carbonaceous material as a strongelectron acceptor on which the above mentioned metals or the alloys aremounted, hence the hydrogen is stored in the form of protons. Therefore,its occupied volume is greatly reduced and a large amount of hydrogencan be stored in the hydrogen-storing carbonaceous material as comparedwith the storage by the conventional chemisorption of hydrogen atoms.That is, the hydrogen is separated into electrons and protons from thestate of atoms, and the electrons are efficiently stored in thehydrogen-storing carbonaceous material so that a large amount of highdensity hydrogen can be finally stored in the state of protons.Accordingly, when the above described metals or the alloys are carriedon the surface of the hydrogen-storing carbonaceous material, thehydrogen can be more efficiently stored and a larger amount of hydrogencan be stored. The above described hydrogen-storing carbonaceousmaterial is light-weight, easily transported, can be repeatedly employedat around room temperature without generating a structural destructionand can be safely handled. Further, the amount of use of a metalliccatalyst such as platinum can be reduced. The carbonaceous material suchas fullerene serving as a starting material can be also produced at alow cost. Further, there can be realized an enhanced practicability thata problem is not found in view of the procurement of resources nor aproblem such as an environmental destruction is generated during a use.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a schematic structure of a fuel cellaccording to an embodiment of the present invention.

FIG. 2 is a graph showing results obtained by measuring the change oftemperature and the mass of the carbon nanofiber according to anembodiment of the present invention.

FIG. 3 is a diagram showing a schematic structure of an alkaline storagebattery (secondary battery) according to an embodiment of the presentinvention.

FIG. 4 is a graph showing the cyclic characteristics of the alkalinestorage battery according to an embodiment of the present invention.

FIG. 5 is a diagram showing a schematic structure of a hydrogen-air fuelcell according to an embodiment of the present invention.

FIG. 6 is a graph showing the discharge characteristics of thehydrogen-air fuel cell according to an embodiment of the presentinvention.

FIG. 7 is a graph showing the discharge characteristics of an anotherhydrogen-air fuel cell according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The fuel cell according to an embodiment of the present invention isprovided with a cathode 1 and an anode 2 arranged so as to be opposed toeach other as shown in FIG. 1. Here, as the cathode 1, an oxygenelectrode is used. As the anode 2, a fuel electrode or a hydrogenelectrode is used. The cathode 1 has a cathode lead 3 and a catalyst 5is dispersed in the cathode or is adhered to the cathode. The anode 2also has an anode lead 6 and a catalyst 7 is dispersed in the anode oris adhered to the anode. A proton conductor 8 is sandwiched in betweenthe cathode 1 and the anode 2. Hydrogen 12 as fuel is supplied to apassage 13 in the side of the anode 2 through an introducing port 11from a hydrogen supply source 10, and discharged from a discharge port14. In the side of the cathode 1, air 15 is supplied to a passage 17from an introducing port 16 and discharged from a discharge port 18.

While the hydrogen 12 serving as the fuel supplied to the passage 13from the introducing port 11 passes the passage 13, protons aregenerated and the generated protons move to the side of the cathode 1together with protons generated in the proton conductor 8. As a result,the protons react with oxygen in the air 15 supplied to the passage 17from the introducing port 16 and directed to the discharge port 18 sothat a desired electromotive force is taken out.

In the present invention, for the hydrogen supply source 10, is employeda hydrogen-stored carbonaceous material obtained by heating acarbonaceous material such as fullerene, carbon nanofiber, carbonnanotube, carbon soot, nanocapsule, bucky onion and carbon fiber, thelike or mixtures thereof under the atmosphere of hydrogen gas and thenstoring hydrogen.

In the fuel cell according to an embodiment of the present invention,since, while the protons are dissociated, the protons supplied from theanode 2 side move to the cathode 1 side in the proton conductor 8, theconductivity of the protons is characteristically improved. Therefore,since a humidifier which has been typically required for conductingprotons is not needed, a system can be simplified and lightened.

Without limitation, examples and comparative examples illustrating theeffectiveness of the present invention are described below.

COMPARATIVE EXAMPLE

A carbon nanofiber with one nanotube fiber whose diameter is about 200mm was manufactured by a CVD method and impurities such as a catalystwere completely removed until purity became 95% or higher before athermobalance measurement was carried out. The carbon nanofiber of 14.3mg thus obtained was accommodated in a sample cup in a thermobalance,and then, initially, the contents in a measurement vessel werecompletely replaced by using nitrogen gas.

Then, hydrogen gas of 1 atmospheric pressure was introduced into themeasurement vessel at a flow velocity of 100 cc per minute, and thecarbon nanofiber was held for 3 hours.

Subsequently, nitrogen gas was introduced again into the measurementvessel to measure the change of the mass of the carbon nanofiber. As aconsequence, the change of the mass was not absolutely recognized and itwas found that hydrogen was not stored.

EXAMPLE 1

A carbon nanofiber was manufactured in the same manner as that of theComparative Example and impurities such as a catalyst were completelyremoved until purity became 95% or higher before a thermobalancemeasurement was carried out.

The carbon nanofiber of 14.3 mg thus obtained was accommodated in asample cup in a thermobalance, and then, initially, the contents in ameasurement vessel were completely replaced by using nitrogen gas. Then,while hydrogen gas of 1 atmospheric pressure was introduced into themeasurement vessel at a flow velocity of 100 cc per minute, thetemperature was raised up to 400° C. at a rate of 60° C. per minute andheld at 400° C. for 3 hours to clean the carbon nanofiber by thehydrogen gas.

Then, after a cleaning operation by the hydrogen gas was finished, thetemperature was lowered to 20° C. After it was recognized that thetemperature reached 20 C, nitrogen gas was introduced again into themeasurement vessel to measure the change of the mass of the carbonnanofiber.

FIG. 2 is a graph showing results obtained by measuring the change oftemperature and the mass of the carbon nanofiber.

As shown in FIG. 2, while the cleaning operation by the hydrogen gas wascarried out, the mass of the carbon nanofiber was gradually decreased.It is recognized that this phenomenon is produced, because the hydrogengas is introduced into the measurement vessel so that, while impuritiessuch as hydrogen, oxygen, functional groups, or the like on the surfaceof the carbon nanofiber are removed, the mass of the carbon nanofiber isgradually decreased due to a larger amount of removed impurities thanthat of the hydrogen adsorbed on the surface of the carbon nanofiber.Further, the rate of decrease of the mass of the carbon nanofiber isreduced around 170 minutes after the hydrogen gas is introduced into themeasurement vessel. It may be estimated that this phenomenon shows thatthe removal of impurities by the hydrogen gas is coming to an end.

On the other hand, when nitrogen gas was introduced into the measurementvessel, it was recognized that the mass of the carbon nanofiber wasgreatly decreased. It may be estimated that this phenomenon shows thathydrogen stored in the carbon nanofiber is discharged. However, sinceall the stored hydrogen is not discharged, it is recognized the decreaseof the mass of the carbon nanofiber after the nitrogen gas is introducedinto the measurement vessel indicates a lower limit value of the amountof hydrogen stored in the carbon nanofiber.

Thus, when the amount of hydrogen stored in the carbon nanofiber wasobtained under these premises, it was recognized that hydrogen of atleast 8.4 wt % was stored in the carbon nanofiber. Here, the amount ofstored hydrogen is a value obtained by dividing the mass of storedhydrogen by the mass of carbon.

As apparent from the Example 1 made pursuant to an embodiment of thepresent invention and the Comparative Example, it was recognized thatthe carbon nanofiber subjected to no process had no hydrogen storagecapacity. On the other hand, while the hydrogen gas of 1 atmosphericpressure was introduced into the measurement vessel at a flow velocityof 100 cc per minute, the temperature was raised up to 400° C. at a rateof 60° C. per minute and held at 400° C. for 3 hours to clean the carbonnanofiber by the hydrogen gas, and accordingly, it was recognized thatthe hydrogen storage capacity of the carbon nanofiber was effectivelyenhanced.

EXAMPLE 2

An alkaline storage battery was manufactured in the following manner.

<Manufacture of Cathode>

Carboxymethyl cellulose of 3 wt % was added to spherical nickelhydroxide of 10 g with the average particle size of 30 mm and cobalthydroxide of 1 g and the mixture was kneaded with water to preparepaste. A porous nickel foam with the porosity of 95% was filled with thepaste, and the porous nickel foam filled with the paste was dried andpressed, and then punched to manufacture a cathode having the diameterof 20 mm and the thickness of 0.7 mm.

<Manufacture of Anode>

Carboxymethyl cellulose of 5% and water were added to thehydrogen-stored carbonaceous material which prepared in accordance withthe Example 1 to prepare kneaded paste. The porous nickel foam with theporosity of 95% was filled with the paste, the porous nickel foam filledwith the paste was dried and pressed, and then punched to manufacture ananode with the diameter of 20 mm and the thickness of 0.5 mm.

<Alkaline Storage Battery>

Then, an alkaline storage battery (secondary battery) schematicallyshown in FIG. 3 was manufactured by using the cathode and the anodemanufactured as described above and potassium hydroxide solution of 7Nas electrolyte solution.

The alkaline storage battery comprises a cathode 1, an anode 2 andelectrolyte solution 21 contained therebetween in a battery vessel 20. Acathode lead 3 and an anode lead 6 are taken outside the battery vessel20 from the respective electrodes.

<Charge and Discharge Performance>

For the alkaline storage battery manufactured as described above, thecharge and discharge test was carried out with 0.1 C, the upper limit of1.4V and the lower limit of 0.8 V. The cyclic characteristics at thattime are shown in FIG. 4.

As apparent from FIG. 4, although it could not be said that a cycle lifewas not sufficient from the viewpoint of structure of the battery, abasic charge and discharge performance could be recognized.

EXAMPLE 3

A hydrogen-air fuel cell was manufactured in the following manner.

<Manufacture of Air Electrode>

The hydrogen-stored carbonaceous material was prepared in accordancewith the Example 1. The hydrogen-stored carbonaceous material andpolymer electrolyte alcoholic solution composed of perfluorosulfonicacid were dispersed in n-butyl acetate to prepare catalyst layer slurry.

On the other hand, a carbon nonwoven fabric with the thickness of 250 mmwas immersed in the emulsion of fluorine water repellent, dried and thenheated at 400° C., so that the carbon nonwoven fabric was subjected to awater repellent process. Subsequently, the carbon nonwoven fabric wascut to the size of 4 cm×4 cm and the catalyst layer slurry prepared asdescribed above was applied to one surface thereof.

<Adhesion of Air Electrode to Polymer Electrolyte Film>

A polymer electrolyte film composed of perfluorosulfonic acid with thethickness of 50 mm was adhered to the surface of the carbon nonwovenfabric to which the catalyst layer was applied, and then, the filmadhered to the nonwoven fabric was dried.

<Manufacture of Hydrogen Electrode>

Carboxymethyl cellulose of 5% and water were added to the samehydrogen-stored carbonaceous material as that used for manufacturing theair electrode to prepare paste. A porous nickel foam with the porosityof 95% was filled with the paste, dried and pressed and the dried andpressed porous nickel foam was cut to the size of 4 cm×4 cm tomanufacture a hydrogen electrode with the thickness of 0.5 mm.

<Manufacture of Hydrogen-Air Fuel Cell>

The hydrogen electrode was superposed on the adhered body of the airelectrode and the perfluorosulfonic acid polymer electrolyte filmobtained as described above by holding the polymer electrolyte filmtherebetween. Both the surfaces thereof were firmly held by Teflonplates with the thickness of 3 mm and fixed by bolts. Many holes withdiameter of 1.5 mm are previously opened on the Teflon plate arranged inthe air electrode side so that air can be smoothly supplied to anelectrode.

The schematic structure of the hydrogen-air fuel cell thus assembled isshown in FIG. 5.

As shown in FIG. 5, in the hydrogen-air fuel cell thus manufactured, ahydrogen electrode 31 and an air electrode 32 are arranged so as to beopposed to each other by locating a polymer electrolyte film 30 betweenthe hydrogen electrode and the air electrode. The outer side of thesemembers is held by a Teflon plate 33 and a Teflon plate 35 provided withmany air holes 34 and all the body is fixed by means of bolts 36 and 36.A hydrogen electrode lead 37 and an air electrode lead 38 arerespectively taken out from the respective electrodes.

<Discharge Characteristics of Hydrogen-Air Fuel Cell>

Then, the discharge characteristics of the hydrogen-air fuel cell wasexamined.

Initially, electric current was supplied in a charging direction withthe current density of 1 mA/cm² to store hydrogen in the hydrogenelectrode. Then, a discharging operation was carried out with thecurrent density of 1 mA/cm². As a result, the discharge characteristicsas shown in FIG. 6 could be obtained and a function as the hydrogen-airfuel cell was recognized.

Further, before the fuel cell was assembled, hydrogen was previouslystored in the hydrogen electrode under the pressure of 100 kg/cm². Thehydrogen electrode thus hydrogen storage was superposed on the adheredbody of the air electrode and the perfluorosulfonic acid polymerelectrolyte film obtained as described above to assemble thehydrogen-air fuel cell. When the discharge characteristic of theobtained fuel cell was measured with the current density of 1 mA/cm²,the discharge characteristic as shown in FIG. 7 was obtained and afunction as the hydrogen-air fuel cell could be also recognized in thiscase.

It is to be understood that the present invention is not limited to theabove described embodiments and Examples and can include any suitablemodification thererof. For example, in the above described embodiments,although the fuel cell using the hydrogen-storing carbonaceous materialand the hydrogen-stored carbonaceous material was described, thehydrogen-storing carbonaceous material and the hydrogen-storedcarbonaceous material according to the present invention in anembodiment are not limited to the fuel cell but also may be widelyapplied to uses for hydrogen storage as well as other batteries such asan alkaline storage battery, a hydrogen-air fuel cell, or the like.

According to the present invention in an embodiment, there can beprovided a hydrogen-storing carbonaceous material which can efficientlystore a large amount of hydrogen, is light-weight and safe, can berepeatedly used and may not possibly generate problems in view ofresources and an environment and a method for producing it, ahydrogen-stored carbonaceous material and a method for producing it, abattery using a hydrogen-stored carbonaceous material and a fuel cellusing a hydrogen-stored carbonaceous material.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A method of producing a hydrogen-storing carbonaceous material, themethod comprising annealing a carbon nanofiber material in a gasatmosphere including hydrogen gas substantially not including a reactivegas as impurity gas at a temperature of about 400° C. and under a gaspressure of 1 atmospheric pressure or, wherein the carbon nanofibermaterial is produced by chemical vapor deposition.
 2. The methodaccording to claim 1, wherein the carbon nanofiber material is heated inthe gas atmosphere that consists essentially of hydrogen gas.
 3. Themethod according to claim 1, wherein the carbon nanofiber material has alarge surface and a structural curvature.
 4. The method according toclaim 3, further comprising a carbonaceous material selected from agroup consisting of fullerene, carbon nanotube, carbon soot,nanocapsule, bucky onion, carbon fiber and mixtures thereof.
 5. A methodof producing a hydrogen-stored carbonaceous material, the methodcomprising annealing a carbon nanofiber material in a gas atmosphereincluding hydrogen gas and substantially including no reactive gas asimpurity gas at a temperature of about 400° C. and under a gas pressureof 1 atmospheric pressure or, wherein the carbon nanofiber material isproduced by chemical vapor deposition.
 6. The method according to claim5, wherein the carbon nanofiber material is heated in the gas atmosphereconsisting essentially of hydrogen gas.
 7. The method according to claim5, wherein the carbon nanofiber material has a large surface and astructural curvature.
 8. The method according to claim 7, furthercomprising a carbonaceous material selected from a group consisting offullerene, carbon nanotube, carbon soot, nanocapsule, bucky onion,carbon fiber and mixtures thereof.